1. Field of the Invention
The present invention generally relates to a dynamo-electric machine having a commutator that includes a plurality of segments.
2. Description of the Related Art
FIG. 7 is a side sectional diagram of a motor 100 for use in an electric power steering system, which is a conventional dynamo-electric machine. This motor 100 for an electric power steering system comprises a cylindrical yoke 101, magnetic poles 102 constituted by permanent magnets, the number of which is 4, and fixed in this yoke 101, a shaft 104 provided in the yoke 101 in such a manner as to be enabled by a bearing 103 to freely rotate, an armature 105 fixed to this shaft 104, a commutator 106 fixed to an end portion of the shaft 104, and brushes 108 made by elastic forces of springs (not shown) to abut against the surface of this commutator 106 and held by brush holders 107.
The armature 105 comprises a core 109 having twenty-two slots, which axially extend, and a winding 111 constituted by a conductor lap-wound through the slots 110.
The hollow-cylinder-like commutator 106 has twenty-two copper segments 112 disposed at equal intervals, and resin materials, placed between adjacent segments 112, for holding and insulating the adjacent segments 112 from each other.
In the four-pole lap-wound motor 100 for use in the electric power steering system, electric current is externally supplied to the wiring 111 through the brushes 108 that abut against the segments 112. Consequently, the armature 105 rotates together with the shaft 104 by electromagnetic action.
FIGS. 8 and 9 are developed plan winding diagrams each illustrating the cylindrical arrangement of the winding 111, the magnetic poles 102, the communicator 106, and the brushes 108 in the direction of rotation so as to explain the positional relation among the mounting positions of these members.
As shown in FIGS. 8-9, the motor 100 for use in an electric power steering system has twenty-two teeth 113, twenty-two segments 112, and four magnetic poles 102. For easy understanding of the connection relation between the coil portions 114 and the segments 112, this figure shows such an arrangement diroughout a range longer than an actual range, that is, a range of more 360 degrees (720 degrees in this case) in terms of a mechanical angle.
Portions designated by characters xe2x80x9cNxe2x80x9d and xe2x80x9cSxe2x80x9d are the magnetic poles 102. Further, parts, each of which is designated by one of symbols xe2x80x9c+xe2x80x9d and xe2x80x9cxe2x88x92xe2x80x9d described at the bottom thereof, are the brushes 108. Rectangles, to which the numbers 1 to 22 described under the characters xe2x80x9cNxe2x80x9d and xe2x80x9cSxe2x80x9d are respectively assigned, are the teeth 113 for defining the slots 110. Further, rectangles described just above the brushes 108, to which the numbers 1 to 22 are respectively assigned, are the segments 112.
As illustrated in FIG. 10, each of the windings 111 of this example is constituted by what is called xe2x80x9cdouble windingxe2x80x9d, in which the two coil portions 114 are parallel-connected between each pair of adjacent ones of the segments 112. FIG. 8 is a winding diagram illustrating the outer (or upper) side winding 111 provided in the radial direction of the core 109 of the armature 105, between the windings. FIG. 9 is a winding diagram illustrating the inner (or lower) side winding 111 provided in the radial direction of the core 109 of the armature 105, between the windings.
The windings 111 constituted by the xe2x80x9cdouble windingxe2x80x9d has advantages over what is called xe2x80x9csingle windingxe2x80x9d in that thinner conductors can be used, and that thus the workability in winding is enhanced.
Incidentally, in the case of each of the coil portions 114 indicated by dotted lines in FIG. 10, each of the brushes 108 is brought into abutting engagement with two of the segment 112, as shown in FIG. 11. Thus, these segments are at equal electric potential. Consequently, the dotted lines indicate that no current flows through the corresponding wring portion 114.
In the case of this example having a total of twenty-two segments 112, twenty-two coil portions are disposed at each of the upper and lower sides of the winding 111. However, instead of inserting the coil portions 114, which are provided correspondingly to the upper and lower sides, into the same slot, such coil portions 114 are inserted into magnetically symmetrical different slots.
That is, the two coil portions 114 are parallel-connected to each other between the adjacent two segments 112. FIG. 12(a) shows one 114B of the coil portions, which is provided at the lower side. FIG. 12(b) shows one 114A of the coil portions, which is provided at the upper side. FIG. 12(c) shows the coil portion 114B, which is provided at the lower side, and the coil portion 114A, which is provided at the upper side. Further, this figure shows that the upper-side coil portion 114A and the lower-side coil portion 114B are apart from each other by 180 degrees in terms of a mechanical angle.
Meanwhile, attention is now focused on an upper-side coil portion 114A and a lower-side coil portion 114B of the winding 111, which respectively have lead parts 115A and 115B connected between the segment No. 12 and the segment No. 13 of the segments 112. The upper-side coil portion 114A is constructed by winding a conductor a plurality of times between a slot 110, which is formed between the tooth No. 10 and the tooth No. 11 of the teeth 113, and another slot 110, which is formed between the tooth No. 15 and the tooth No. 16 of the teeth 113. Thus, this coil portion 114A is placed nearly just above the segment No. 12 and the segment No. 13 of the segments 112. On the other hand, the lower-side coil portion 114B is constructed by winding a conductor a plurality of times between a slot 110, which is formed between the tooth No. 21 and the tooth No. 22 of the teeth 113, and another slot 110, which is formed between the tooth No. 4 and the tooth No. 5 of the teeth 113. Thus, this coil portion 114B is placed nearly just above the segment No. 1 and the segment No. 2 of the segments 112. That is, the upper-side coil portion 114A and the lower-side coil portion 114B, which employ the segment No. 12 as the common start point and also employ the segment No. 13 as the common end point, are apart from each other by 180 degrees in terms of a mechanical angle.
With such an arrangement, the coil portions 114 rectified with the same timing are always disposed at positions at which mechanical balance is provided, even when inconvenience occurs at the brush 108 at one side or when a subtle deviation in characteristics is caused owing to individual difference. Thus, vibrations due to electromagnetic forces are suppressed.
In the motor 100 of the aforementioned configuration for use in an electric power steering system, the coil portions 114 are always disposed at positions at which mechanical balance is provided, so that vibrations due to electromagnetic forces are suppressed. However, the motor 100 of the aforementioned configuration has drawbacks in that this motor cannot prevent a circulating current from flowing through the brushes 108 by way of electric circuit portions owing to the difference among the voltage induced in the circuit portions among the brushes 108 of the winding, and that magnetic-attraction-force imbalance occurs owing to the difference in the number of coil portions among the circuit portions.
The present invention is created to eliminate the aforementioned drawbacks. Accordingly, an object of the present invention is to provide a dynamo-electric machine that has the coil portions disposed at positions at which mechanical balance is provided, and thus can suppress vibrations due to electromagnetic forces, and that can suppress vibrations caused by imbalance due to electromagnetic forces and that also can suppress imbalance in magnetic attraction forces generated owing to the difference in the number of coil portions among electric circuit portions.
To this end, according to the present invention, there is provided a dynamo-electric machine comprising: a yoke; magnetic poles fixed in the yoke; a shaft rotatably provided in the yoke; an armature having a winding consisting of a plurality of coil portions each formed by lap-winding a conductor between a corresponding pair of slots formed in an outer circumferential surface portion of a core fixed to the shaft in such a way as to extend in an axial direction thereof; a commutator fixed to an end portion of the shaft and having a plurality of segments to which both end sections of the coil portions are electrically connected; brushes made to respectively abut against the surfaces of the segments of the commutator; and equalizers for connecting the segments, which are to be at equal electric potential, to each other, wherein n (incidentally, xe2x80x9cnxe2x80x9d is a common divisor of the number of the magnetic poles and the number of the slots and equal to or more than 2) of the coil portions are parallel-connected between said segments, and wherein the coil portions are disposed in such a manner as to be symmetrical with respect to a mechanical angle of 360 degrees.